The appearance of filamentous material structurally similar to actin has been observed in myocytes in myocardial infarcts after infusion of glucose-insulin-potassium (GIK). The filaments arise from the region of the cell membrane in structurally damaged cells and in normal cells adjacent to the infarct and appear to represent repair of the contractile proteins in the damaged cells and to represent sarcomerogenesis in the normal cells adjacent to the infarct. Similar filaments occur following isoproterenol induced necrosis; in infarcts following administration of adenosine and in acute experimental hypertrophy. We plan to utilize the technique of high resolution autoradiography to determine if the filaments represent new protein synthesis or are a degenerative process. BIBLIOGRAPHIC REFERENCES: Sybers, H. D., J. Ingwall, M. DeLuca, and L. Nimmo. Fetal mouse heart in organ culture. Lab. Invest. 32: 157-162, 1975. Ingwall, J. S., M. A. DeLuca, H. D. Sybers and K. Wildenthal. Fetal mouse hearts: A model for studying ischemia (ATP content/Lysosomal Enzymes/Cardiac Ultrastructure. Proc. Nat. Acad. Sci. USA 72: 2809-2813, 1975.